Inwardly burning surface stabilized gas premix burner

ABSTRACT

The burner ( 100 ) comprises a cylindrical porous substrate ( 110 ); and an end cap ( 130 ) at a first end of the cylindrical porous substrate ( 110 ). The cylindrical porous substrate ( 110 ) is provided for flow of a premix of combustible gas and air from the outside of the cylindrical porous substrate ( 110 ) through the pores of the cylindrical porous substrate ( 110 ) to an interior cavity ( 140 ), for the combustible gas to be combusted on the inner surface of the cylindrical porous substrate ( 110 ) thereby generating hot gas. The burner has an opening ( 182 ) at the second end of the cylindrical porous substrate ( 110 ) to exit the hot flue gas out of the interior cavity ( 140 ). The cylindrical porous substrate ( 110 ) has a higher permeability section ( 170 ), located at the opening ( 182 ) at the second end. The higher permeability section ( 170 ) has a lower resistance to gas flow than other sections of the cylindrical porous substrate ( 110 ).

TECHNICAL FIELD

The invention relates to the field of inwardly burning surface stabilized gas premix burners. A surface stabilized gas premix burner is a burner in which combustion occurs on a porous surface, after a premix of combustible gas and air has flown through pores of the porous surface.

BACKGROUND ART

US2012/247444A1, WO2009/151420A1 and U.S. Pat. No. 8,616,194B2 disclose examples of inwardly burning surface stabilized gas premix burners. WO2009/151420A1 describes a burner comprising a body defining an interior cavity and a burner surface located in the body and defining an interior cavity. A diffusing surface is located on an exterior portion of the body. Ports are provided on the body extending through the diffusing and burner surfaces, configured to provide fluid communication between the interior cavity and ambient air outside the body. An opening is provided larger than at least one of the ports in order to provide fluid communication between the interior cavity and a space outside of the body.

As is illustrated in U.S. Pat. No. 8,616,194B2, inwardly burning surface stabilized gas premix burner can advantageously be used in furnace air heaters.

DISCLOSURE OF INVENTION

It is an objective of the invention to provide an inwardly burning surface stabilized gas premix burner with improved lifetime.

A first aspect of the invention is a burner. The burner comprises a cylindrical porous substrate; and an end cap at a first end of the cylindrical substrate. The cylindrical porous substrate and the end cap enclose an interior cavity. The cylindrical porous substrate is provided for flow of a premix of combustible gas and air from the outside of the cylindrical porous substrate through the pores of the cylindrical porous substrate to the interior cavity, for the combustible gas to be combusted on the inner surface of the cylindrical porous substrate thereby generating hot gas. The burner has an opening at the second end of the cylindrical porous substrate, for allowing the hot gas to exit the interior cavity. Preferably, the opening has a circular shape, preferably with diameter at least 50% of the internal diameter of the interior cavity. The cylindrical porous substrate has a higher permeability section. The higher permeability section is located at the opening at the second end of the cylindrical porous substrate. Preferably, the higher permeability section forms the second end of the cylindrical porous substrate. The higher permeability section has a lower resistance to gas flow than other sections of the cylindrical porous substrate; preferably than all the other regions of the cylindrical porous substrate.

Inwardly burning surface stabilized gas premix burners have all the heat generated by the combustion concentrated in the inner cavity, before the heat is evacuated via the hot gas through the opening at the second end. The amount of heat present in the inner cavity poses lifetime issues to such burners. The burner of the invention showed the surprising result that it has a longer lifetime. The long lifetime seems to be achieved by avoiding that parts of the burner get excessively hot when the burner is in use. This result is the more surprising as locally near the opening at the second end more combustible gas will be provided for combustion.

In a preferred embodiment, the higher permeability section comprises or consists out of an annular section of the cylindrical porous substrate. Preferably the annular section has a height of at least 3% of the diameter of the cylindrical porous substrate. More preferably at least 10%, even more preferably at least 15%. And preferably less than 30%, more preferably less than 20%.

Preferably, the annular section is provided at the second end of the cylindrical porous substrate; more preferably the annular section provides the second end of the cylindrical porous substrate.

In a preferred embodiment, the cylindrical porous substrate has a constant resistance to gas flow outside the higher permeability section.

In a preferred embodiment, the cylindrical porous substrate has a constant resistance to gas flow in the higher permeability section.

In a preferred burner, the cylindrical porous substrate comprises a first porous substrate present over the full height of the cylindrical porous substrate. Outside the higher permeability section of the cylindrical porous substrate the inner side of the first porous substrate is covered with a second porous substrate. In the higher permeability section when the burner is in use combustion occurs on the inner surface of the first porous substrate. The first porous substrate can e.g. be a woven wire mesh or a perforated plate or an expanded metal sheet. The second porous substrate can e.g. be a second woven wire mesh, a second perforated plate, a second expanded metal sheet, a textile fabric (e.g. a woven fabric, a knitted fabric, a braided fabric) comprising yarns comprising a plurality of metal fibers in the cross section of the yarns, a sintered powder object, or a sintered fiber object (e.g. sintered metal fibers). In such embodiments, when the higher permeability section comprises or consists out of an annular section of the cylindrical porous substrate, the annular section preferably has a height of at least 3% of the diameter of the cylindrical porous substrate, and more preferably at least 10%; and preferably less than 15%.

Preferably, the second porous substrate is bonded onto the first porous substrate by means of welding. Preferably the welding is soft welding. Soft welding is performed such that when pulling the second porous substrate from the first porous substrate, the soft welded bonds between both substrates give way rather than that breakages occur inside one the porous substrates itself. The test method to determine that the burner deck is soft welded, is pulling in peel-off mode: an edge portion of the second porous substrate is removed from the first porous substrate, and folded over 180°. Pulling the second porous substrate is then done by hand or using pliers, wherein the pulling force is exerted parallel with the first porous substrate, in a direction of 180° to the first porous substrate. In pulling, the force builds up until the second porous substrate is progressively peeled off from the first porous substrate. Within the limits of the described “pulling in peel-off mode” the conclusion whether or not the second porous substrate is soft-welded to the first porous substrate is independent of further parameters. Soft welding has the benefit that long lifetime of the cylindrical porous substrate is obtained. This is a surprising result, as the bonding in soft welding is certainly less strong than when standard welding is used in which stronger bonds between both substrates is obtained. It is believed that the soft welding has a positive effect on the combustion properties, resulting in the longer lifetime of the cylindrical porous substrate, and hence in a longer lifetime of the burner. In a more preferred embodiment, the second porous substrate covers the inside of the first porous substrate from the first end of the cylindrical porous substrate up to a certain distance from the end of the first porous substrate at the second end of the cylindrical porous substrate.

In a preferred embodiment, the cylindrical porous substrate comprises a first porous substrate. The inner side of the first porous substrate is covered with a second porous substrate. The second porous substrate is a woven, knitted or braided fabric comprising stainless steel fibers. The higher permeability section is provided by differences in the structure of the fabric compared to outside the higher permeability section.

The first porous substrate can e.g. be a woven wire mesh or a perforated plate or an expanded metal sheet. The second porous substrate can e.g. be a second woven wire mesh, a second perforated plate, a second expanded metal sheet, a textile fabric (e.g. a woven fabric, a knitted fabric, a braided fabric) comprising yarns comprising a plurality of metal fibers in the cross section of the yarns, a sintered powder object, or a sintered fiber object (e.g. sintered metal fibers). In such embodiments, when the higher permeability section comprises or consists out of an annular section of the cylindrical porous substrate, the annular section preferably has a height of at least 3% of the diameter of the cylindrical porous substrate, and more preferably at least 10%; and preferably less than 15%.

Preferably, the second porous substrate is bonded onto the first porous substrate by means of welding. Preferably the welding is soft welding. As an example of embodiments wherein the higher permeability section is provided by differences in the structure of the fabric compared to outside the higher permeability section, the fabric can be compressed to a lower thickness outside the higher permeability section compared to the thickness in the higher permeability section. A lower thickness of the fabric results in lower permeability. Preferably, the thickness of fabric is in the higher permeability section at least 40%, more preferably at least 50%, even more preferably at least 60% higher, even more preferably at least 100% higher and still even more preferred 150% higher than the average thickness outside the higher permeability section.

In another example of embodiments wherein the higher permeability section is provided by differences in the structure of the fabric compared to outside the higher permeability section, the fabric differs in yarn density in order to create the section with different permeability in the fabric, e.g. the fabric could be a woven fabric with lower weft density in the higher permeability section than outside the higher permeability section.

In a further preferred embodiment, the second porous substrate is a textile fabric comprising yarns. The yarns comprise a plurality of metal fibers in the cross section of the yarns. The metal fibers in the yarns can be continuous filaments or can be discrete length fibers. Further preferred are stainless steel fibers as metal fibers, e.g. fibers out of a Fe, Cr and Al comprising alloy such as FeCrAlloy. Preferred fabrics are woven fabrics, knitted fabrics or braided fabrics. Further preferred are weft knitted fabrics.

In a more preferred embodiment, the second porous substrate is a weft knitted fabric. The weft direction of the weft knitted fabric is provided in the circumferential direction of the cylindrical porous substrate.

In another more preferred embodiment, the second porous substrate is a weft knitted fabric. The weft direction of the weft knitted fabric is provided in the axial direction of the cylindrical porous substrate.

In a preferred embodiment of the invention, the cylindrical porous substrate has a higher porosity in the higher permeability section than in other sections of the cylindrical porous substrate. In such embodiments, when the higher permeability section comprises or consists out of an annular section of the cylindrical porous substrate, the annular section preferably has a height of at least 3% of the diameter of the cylindrical porous substrate, and more preferably at least 15%; and preferably less than 30%.

In a more preferred embodiment, the cylindrical porous substrate comprises or consists out of a perforated plate. The porosity of the plate is the percentage of the surface area which is open for gas flow passage. In the higher permeability section, the higher porosity is provided by means of a higher number of perforations per unit of surface area and/or by larger perforations of a larger cross sectional area. Preferably, the porosity in the higher permeability section is in relative terms at least 20% higher than outside the higher permeability section, more preferably at least 40% higher than outside the higher permeability section, more preferably at least 60% higher than outside the higher permeability section. And even more preferably the porosity in the higher permeability section is less than double the permeability outside the higher permeability section; even more preferably less than 60% higher than outside the higher permeability section.

The porosity in the higher permeability section is e.g. between 15 and 33%. The porosity outside the higher permeability section is e.g. between 14 and 17%. It is also possible to have a section of the perforated plate at the end cap, wherein that section has a porosity lower than the porosity outside the higher permeability section, but preferably at least having 7% porosity.

A preferred burner comprises a flange at the second end of the cylindrical porous substrate. In use, hot flue gas exits the interior cavity via the central opening in the flange. The flange can be provided to allow mounting the burner into a supporting structure, e.g. inside a heat exchanger. To this end, the flange can be provided with holes for mounting the flange to a supporting structure, e.g. by means of bolts.

It is also possible that the flange is formed by a raised collar in the plate onto which the burner is mounted.

It is also possible that the flange is formed by mechanical deformation of material of the cylindrical porous surface, preferably by deformation of the first porous surface. An example of such embodiment is where the first porous surface is formed by a perforated metal plate formed into cylindrical shape, and wherein the end of the metal plate is deformed to form a flange.

In a further preferred burner, the flange is attached to the cylindrical porous substrate at the inner side of the cylindrical porous substrate; preferably by means of welding. An Inwardly burning surface stabilized gas premix burner according to the prior art showed to have further reduced lifetime when the flange is attached at the inner side to the cylindrical porous substrate, way of attachment which facilitates manufacturing operations. Surprisingly however, the inventive burner with the flange attached to the cylindrical porous substrate at the inner side of the cylindrical porous substrate showed excellent lifetime.

In a preferred burner, the end cap comprises perforations for the passage of premix combustible gas and air through the end cap to the inside of the interior cavity for being combusted inside the interior cavity. Such perforations can e.g. be circular or slit shaped, or a combination of circular perforations and slit shaped perforations. In a preferred embodiment, the perforations include circular perforations with a diameter less than 0.9 mm, e.g. a diameter 0.8 mm. In embodiments where slit shaped perforations are provided, slits preferably have a width of less than 0.6 mm; e.g. 0.5 mm.

More preferred is a burner wherein the end cap comprises perforations in a first area around the centre point of the end cap. The first area has a diameter of less than 60%, preferably of less than 50% of the diameter of the end cap. The end cap further comprises perforations in a second area, wherein the second area is located outside the area around the centre point of the end cap; wherein the area has a diameter of more than 75%, preferably of more than 80% of the diameter of the end cap. The end cap is not perforated in the area between the first area and the second area. Preferably the perforations in the second area are one or two rows of perforations in a circular configuration around the centre point of the end cap.

Although the end cap can be connect onto the cylindrical porous substrate at the inner side of the cylindrical porous substrate; preferably, the end cap is connected onto the cylindrical porous substrate at the outer side of the cylindrical porous substrate. Such embodiment—wherein the end cap is connected onto the cylindrical porous substrate at the outer side of the cylindrical porous substrate—synergistically adds to the longer lifetime as it allows that the burner dimensions can be better maintained during manufacturing of the burner. Burner dimensions are important for the proper operation of the burner. Improper operation of the burner could lead to local overheating of the burner, and breakdown of the burner leading to shorter lifetime of the burner. Preferably, the end cap is connected onto the cylindrical porous substrate by means of welding.

A second aspect of the invention is a heating device for heating a fluid. The heating device comprises at least two of burners as in the first aspect of the invention. Preferably, the burners are linearly aligned in the heating device. The fluid to be heated can e.g. be air. The heating device can be a furnace air heater. In a preferred furnace air heater, each of the burners is provided to exit hot gas through the opening at the second end of the burner into a specific tube of a tubular heat exchanger.

BRIEF DESCRIPTION OF FIGURES IN THE DRAWINGS

FIG. 1 shows an example of a burner according to the invention.

FIGS. 2 and 3 show cross sections of burners according to the invention.

FIG. 4 shows an example of an end cap that can be used in burners according to the invention.

FIG. 5 shows a heating device according to the second aspect of the invention.

MODE(S) FOR CARRYING OUT THE INVENTION

FIG. 1 shows an example of a burner 100 according to the invention.

FIG. 2 shows a section of the burner taken according to the plane 2-2 parallel with and through the central axis of the burner. The burner 100 comprises a cylindrical porous substrate 110; and an end cap 130 at a first end of the cylindrical substrate. The cylindrical porous substrate 110 and the end cap 130 enclose an interior cavity 140.

The end cap 130 of the exemplary burner 100 has perforations 132 for the passage of premix combustible gas and air through the end cap 130 to the inside of the interior cavity 140 for being combusted inside the interior cavity 140. The end cap 130 of the exemplary burner 100 is connected onto the porous substrate at the outer side of the porous substrate.

The cylindrical porous substrate 110 is provided for flow of a premix of combustible gas and air from the outside of the cylindrical porous substrate 110 through the pores of the cylindrical porous substrate to the interior cavity 140, for the combustible gas to be combusted on the inner surface of the cylindrical porous substrate thereby generating hot gas. The burner 100 has an opening 182 at the second end of the cylindrical porous substrate, for allowing the hot gas to exit the interior cavity. In the example shown, the burner 100 comprises a flange 180 at the second end. The opening 182 is provided in the flange 180. In the exemplary burner 100, the flange 180 is attached to the cylindrical porous substrate 110 at the inner side of the cylindrical porous substrate 110, by means of welding. The flange 180 can be used to mount a burner to a support structure.

The cylindrical porous substrate 110 of the exemplary burner 100 comprises a first porous substrate 112 present over the full height of the cylindrical porous substrate 110. Outside the higher permeability section 170 of the cylindrical porous substrate 110 the inner side of the first porous substrate 112 is covered with a second porous substrate 114. Due to fact that outside the higher permeability section 170 of the cylindrical porous substrate 110, premix gas and air needs to flow through the first porous substrate 112 and through the second porous substrate 114, the resistance to gas flow is higher and therefore, the gas permeability is lower. In the higher permeability section 170, combustion will occur on the inner surface of the first porous substrate 112. Outside the higher permeability section 170, combustion will occur on the inner surface of the second porous substrate 114. In the example, the higher permeability section consists out of annular section of the cylindrical porous substrate 110; however other shapes of the higher permeability sections are possible.

Preferred examples for the first porous substrate are a woven metal wire mesh or a perforated metal plate. Preferred example for the second porous substrate—that can be combined with any of the first porous substrates—is a textile fabric comprising yarns, wherein the yarns comprise a plurality of metal fibers in the cross section of the yarns. It is preferred when the textile fabric is soft welded onto the first porous substrate. A specific example for the second porous substrate is a weft knitted fabric out of yarns spun from FeCrAlloy fibers. As an example, the weft direction of the weft knitted fabric can be provided in the circumferential direction of the cylindrical porous substrate. As an alternative example, the weft direction of the weft knitted fabric can be provided in the axial direction of the cylindrical porous substrate.

FIG. 3 shows the section of an alternative burner 300 according to the invention. The burner 300 is to a large extent similar to the burner shown in FIGS. 1 and 2. Parts in FIG. 3 with the same reference numeral as in FIGS. 1 and 2 are identical as in the burner shown in FIGS. 1 and 2. The burner 300 in FIG. 3 differs from the burner shown in FIG. 2 in that the cylindrical porous substrate 316 is formed out of a perforated metal plate welded at its contact edge to form the cylindrical porous substrate 316. The perforated metal plate, and thus the cylindrical porous substrate, has a higher porosity in the higher permeability section 370 than in its other sections 374. In the example, the higher permeability section 370 is an annular section of the cylindrical porous substrate 316, at the second end of the cylindrical porous substrate 316. The perforations in the perforated metal plate can be circular perforations and/or slits. Preferably, circular perforations have a diameter of less than 0.9 mm, e.g. 0.8 mm. Slits preferably have a width of less than 0.6 mm; e.g. 0.5 mm. The higher porosity in the higher permeability section 370 is e.g. provided by means of a higher number of perforations (circular perforations and/or slits) than in the other sections 374 of the cylindrical porous substrate 316. The porosity in the higher permeability section 370 is e.g. 26%. Outside the higher permeability section, the porosity of the perforated metal plate is e.g. 15%. The perforated metal plate can also have a small section at the end cap, wherein the section has a porosity of e.g. 9%.

FIG. 4 shows an example of an end cap 430 that can be used in the invention. The end cap 430 has a diameter D. the end cap 430 comprises perforations 434 in a first area around the centre point of the end cap. The first area has a diameter D1 of less than 60% of the diameter of the end cap. The end cap 430 comprises perforations 436 in a second area. The second area is located outside the area around the centre point of the end cap; wherein the area has a diameter D2 of more than 75%. The end cap 430 is not perforated in the area between the first area and the second area. The perforations of in the first area and the perforations in the second area e.g. have a diameter of 0.8 mm.

FIG. 5 shows a heating device 500 for heating a fluid according to the second aspect of the invention. The heating device 500 comprises a number of burners 100 as in the first aspect of the invention. The burners 100 are linearly aligned in the heating device 500. The flanges 580 of the burners 500 are attached to a mounting plate 592. The burners are provided in a premixing chamber 594, which is provided with walls 596. A premix of combustible gas and air in fed (see arrow 598) into the premixing chamber 594 through one of the walls of the premixing chamber. Hot gas generated by combustion of the premix gas on the inner surface of the cylindrical porous substrate 510 flows from the interior cavity 140 of the burner 100 through opening 582 into a tube 590, via the combustion chamber 597 provided between the burners 100 and the tubes 590. Each of the burners is provided to exit hot gas through the opening at the second end of the burner into a specific tube of a tubular heat exchanger. The heating device can be a furnace air heater. 

1-15. (canceled)
 16. A burner comprising, a cylindrical porous substrate; an end cap at a first end of the cylindrical substrate; wherein the cylindrical porous substrate and the end cap enclose an interior cavity; wherein the cylindrical porous substrate is provided for flow of a premix of combustible gas and air from the outside of the cylindrical porous substrate through the pores of the cylindrical porous substrate to the interior cavity, for the combustible gas to be combusted on the inner surface of the cylindrical porous substrate thereby generating hot gas; wherein the burner has an opening at the second end of the cylindrical porous substrate, for allowing the hot gas to exit the interior cavity; wherein the cylindrical porous substrate has a higher permeability section, wherein the higher permeability section is located at the opening at the second end; and wherein the higher permeability section has a lower resistance to gas flow than other sections of the cylindrical porous substrate.
 17. A burner as in claim 16, wherein the higher permeability section comprises or consists out of an annular section of the cylindrical porous substrate.
 18. A burner as in claim 16, wherein the cylindrical porous substrate comprises a first porous substrate present over the full height of the cylindrical porous substrate; wherein outside the higher permeability section of the cylindrical porous substrate the inner side of the first porous substrate is covered with a second porous substrate; and wherein in the higher permeability section when the burner is in use combustion occurs on the inner surface of the first porous substrate.
 19. Burner as in claim 16, wherein the cylindrical porous substrate comprises a first porous substrate; wherein the inner side of the first porous substrate is covered with a second porous substrate; wherein the second porous substrate is a woven, knitted or braided fabric comprising stainless steel fibers; and wherein the higher permeability section is provided by differences in the structure of the fabric compared to outside the higher permeability section.
 20. Burner as in claim 18, wherein the second porous substrate is a textile fabric comprising yarns, and wherein the yarns comprise a plurality of metal fibers in the cross section of the yarns.
 21. Burner as in claim 18, wherein the second porous substrate is a weft knitted fabric; and wherein the weft direction of the weft knitted fabric is provided in the circumferential direction of the cylindrical porous substrate.
 22. Burner as in claim 18, wherein the second porous substrate is a weft knitted fabric; and wherein the weft direction of the weft knitted fabric is provided in the axial direction of the cylindrical porous substrate.
 23. Burner as in claim 16; wherein the cylindrical porous substrate has a higher porosity in the higher permeability section than in other sections of the cylindrical porous substrate.
 24. Burner as in claim 23, wherein the cylindrical porous substrate comprises or consists out of a perforated plate; and wherein in the higher permeability section, the higher porosity is provided by means of a higher number of perforations per unit of surface area and/or by larger perforations of a larger cross sectional area.
 25. Burner as claim 16, wherein the burner comprises a flange at the second end of the cylindrical porous substrate, and wherein in use, hot flue gas exits the interior cavity via the central opening in the flange.
 26. Burner as in claim 25, wherein the flange is attached to the cylindrical porous substrate at the inner side of the cylindrical porous substrate.
 27. Burner as in claim 16, wherein the end cap comprises perforations for the passage of premix combustible gas and air through the end cap to the inside of the interior cavity, for the premix combustible gas to be combusted inside the interior cavity.
 28. Burner as in claim 27, wherein the end cap comprises perforations in a first area around the centre point of the end cap; wherein the first area has a diameter of less than 60% of the diameter of the end cap; wherein the end cap comprises perforations in a second area, wherein the second area is located outside the area around the centre point of the end cap; with diameter more than 75% of the diameter of the end cap; and wherein the end cap is not perforated in the area between the first area and the second area.
 29. Burner as in claim 16, wherein the end cap is connected onto the cylindrical porous substrate at the outer side of the cylindrical porous substrate.
 30. Heating device for heating a fluid, wherein the heating device comprises at least two burners as in claim
 16. 